It is well known that an aircraft in flight is commanded through three axes of control, namely the pitch, roll and yaw axes. Control surfaces on the aircraft structure are thus commanded by a pilot (or autopilot if so equipped) to move in appropriate directions so the aircraft attitude may be controllably adjusted relative to such axes of control to thereby allow control over the aircraft's flight path. In conventional aircraft, control of the aircraft about the yaw axis is typically accomplished through foot pedals in the aircraft cockpit which when manipulated by the pilot's feet cause an aircraft rudder to be deflected and thereby yaw the aircraft in the desired direction. Thus, pressing the right rudder pedal will cause the rudder control surface to be deflected rightward thereby responsively causing the aircraft to yaw rightward. Conversely, pressing the left rudder pedal will cause the rudder control surface to be deflected leftward thereby responsively causing the aircraft to yaw leftward.
Aircraft which are provided with reversible flight controls (that is, a flight control system wherein movement of the control surface will back-drive the pilot's control in the cockpit) may have certain limitations. For example, such reversible flight controls may have maximum rudder pedal force requirements that can lead to severe restrictions at minimum aircraft control speed (Vmc) thereby causing significant degradation on aircraft field length performance. One traditional aerodynamic solution to maximum rudder pedal force requirements is to employ the rudder tab surface automatically under autotab operation so as to avoid Vmc rudder force restrictions. However, excessive autotab gearing values may cause non-linearity of the pedal forces and also may reduce rudder efficiency.
Rudder control systems are also desirable which assist the pilot to compensate for thrust asymmetry caused by an engine failure. Specifically, it is desirable to allow a pilot to command substantial rudder deflection in an asymmetrical thrust situation so as to counteract adverse aircraft yaw that is caused by the thrust asymmetry (i.e., so as to achieve a controllable side-slip attitude). The advantages of such a system, as compared to a rudder autotab system, include rudder authority maintenance and a lower susceptibility to pedal force relief.
It would be desirable, however, if rudder boost systems were provided which could function so as to limit pilot-induced rudder force during symmetrical thrust conditions (thereby effectively providing maximum rudder input force) while at the same time allowing for such maximum forces to be exceeded when needed during an asymmetrical thrust condition. Such systems would therefore allow maximum rudder input to be observed during symmetrical thrust conditions and prevent for example adverse Vmc aircraft attitudes, yet allow the pilot to obtain the sufficient yaw to achieve an acceptable sideslip angle and maintain flight control during asymmetrical thrust conditions, for example during an engine-out situation. It is towards fulfilling such needs that the present invention is directed.
According to some implementations of the present invention, rudder assist mechanisms are provided which are capable of being operably connected to an aircraft's rudder control system. The rudder assist mechanisms most preferably have over-the-center spring biasing functions so as to cause either substantially no spring force (i.e., when the linkage is over the spring-bias center) or substantially all spring force (i.e., when the linkage is left or right of the spring-bias center) to be exerted on the rudder control system.
One implementation of the invention includes a rudder assist mechanism for operable interconnection with a rudder control system of an aircraft rudder control surface, the rudder assist mechanism comprising a control spring assembly, and a linkage assembly which operably connects the control spring assembly to the rudder control assembly. The linkage assembly is moveable operably between a null position wherein substantially no spring force of the control spring assembly is transferred to the rudder control system by the linkage assembly, and right and left spring-biased positions wherein right and left spring forces of the control spring assembly are transferred to the rudder control system, respectively.
The null position may establish a dead zone of rudder deflection within a selected range of right and left rudder control surface deflection angles. Thus, right and left spring forces may be transferred to the rudder control system when the rudder control surface is deflected at an angle which exceeds the selected range of deflection angles, but not be transferred to the rudder control system when the rudder control surface is deflected at an angle which is within the selected range of deflection angles.
Some implementations of the rudder assist mechanism may include an actuator unit which is operably capable of moving the rudder assist mechanism (e.g., the control spring assembly and the linkage assemble connected thereto) between a thrust symmetrical mode (TSM) condition and a thrust asymmetrical mode (TAM) condition. In response to the actuator unit operably moving the rudder assist mechanism into the TSM condition, the right and left spring forces may be transferred to the rudder control system so as to cause a greater force to be exerted on the rudder control system to effect right and left deflections of the rudder control surface which exceed the selected range of deflection angles. However, in response to the actuator unit operably moving the rudder assist mechanism into the TAM condition, the right and left spring forces may be transferred to the rudder control system so as to cause a lesser force to be exerted on the rudder control system to effect right and left deflections of the rudder control surface which exceed the selected range of deflection angles.
Certain embodiments of the rudder assist mechanism may comprise an engine monitor which issues a signal to the actuator unit indicative of an abnormal thrust condition so as to cause the actuator unit to responsively move the spring and linkage assemblies from the TSM condition to the TAM condition.
According to some implementations, the rudder assist mechanisms may include a control spring assembly having (i) a housing, (ii) a support fork pivotally connected to the housing, (iii) a tension spring having one end pivotally connected to the support fork and an opposite end connected operably to the actuator unit, and (iv) a compression spring having one end pivotally connected to the support fork and an opposite end journally connected to the housing, and a control rod pivotally interconnecting the support fork and the rudder control system.
Each of the tension spring, the compression spring and the control rod may be pivotally connected at a common pivot axis to the support fork. In certain implementations, the control spring assembly will comprise a pair of tension springs each of which has one end connected pivotally to the support fork and an opposite end connected operably to the actuator unit. The actuator unit may therefore include linearly reciprocal actuator rod, and an actuator bell crank connected at one end to the actuator rod and at an opposite end to the compression spring.
An aircraft is provided according to other implementations of the invention and comprises a rudder control surface, a reversible rudder control system operably connected to the rudder control surface to provide physical feedback to a pilot in command of the rudder control surface, and a rudder assist mechanism connected operably to the rudder control system. The rudder assist mechanism may comprise a control spring assembly, and a linkage assembly which operably connects the control spring assembly to the rudder control assembly. According to such implementations, the linkage assembly is therefore preferably moveable operably between a null position wherein substantially no spring force of the control spring assembly is transferred to the rudder control system by the linkage assembly, and right and left spring-biased positions wherein right and left spring forces of the control spring assembly are transferred to the rudder control system, respectively.
The aircraft may comprise an engine monitor and the rudder assist mechanism may further comprise an actuator unit which is operably capable of moving the rudder assist mechanism between a TSM condition and a TAM condition in response to receiving a signal from the engine monitor indicative of an abnormal engine thrust. Preferably, in such implementations, the null position of the rudder assist mechanism establishes a dead zone of rudder deflection within a selected range of right and left rudder control surface deflection angles, and wherein the right and left spring forces are transferred to the rudder control system when the rudder control surface is deflected at an angle which exceeds the selected range of deflection angles.
Other implementations of the invention include methods of providing rudder assist to a rudder control system of an aircraft rudder control surface. Thus, according to certain embodiments, the method will include providing a rudder assist mechanism comprised of a control spring assembly and a linkage assembly, and operably interconnecting the control spring assembly to the rudder control system with a linkage assembly so as to allow the linkage assembly to be moveable operably between a null position wherein substantially no spring force of the control spring assembly is transferred to the rudder control system by the linkage assembly, and right and left spring-biased positions wherein right and left spring forces of the control spring assembly are transferred to the rudder control system, respectively.
In some implementations, the method includes providing the null position of the linkage assembly so as to establish a dead zone of rudder deflection within a selected range of right and left rudder control surface deflection angles, and wherein the right and left spring forces are transferred to the rudder control system when the rudder control surface is deflected at an angle which exceeds the selected range of deflection angles.
The rudder assist mechanism may be caused to assume one of a TSM condition and a TAM condition. According to some aspects, the method includes monitoring a performance parameter of an aircraft engine; issuing a signal to the rudder assist mechanism in response to detecting an abnormal performance parameter of the monitored engine which is indicative of an asymmetrical thrust condition, and causing the rudder assist mechanism to move respectively between the TSM condition and the TAM condition in response to the absence or presence of the signal being issued.
In such implementations, the rudder assist mechanism may comprise an actuator unit which receives the signal indicative of the asymmetrical thrust condition and which is operably connected to the rudder assist mechanism, wherein in the absence of the signal the method comprises causing the actuator to position the rudder assist mechanism in the TSM condition, and wherein in response to receiving the signal, the method comprises causing the actuator unit to move the rudder assist mechanism from the TSM condition to the TAM condition. The rudder mechanism may therefore be caused to assume the TSM condition in the absence of receiving the signal indicative of the asymmetrical thrust condition such that when in the TSM condition, the right and left spring forces of the rudder assist mechanism are transferred to the rudder control system so as to cause a greater force to be exerted on the rudder control system to effect right and left deflections of the rudder control surface which exceed the selected range of deflection angles. Alternatively or additionally, the rudder assist mechanism may be caused to assume the TAM condition in response to receiving the signal, wherein when in the TAM condition, the right and left spring forces are transferred to the rudder control system so as to cause a lesser force to be exerted on the rudder control system to effect right and left deflections of the rudder control surface which exceed the selected range of deflection angles. Thus, the rudder assist mechanism may further comprise an engine monitor which issues a signal to the actuator unit indicative of an abnormal thrust condition so as to cause the actuator unit to responsively move the spring and linkage assemblies from the TSM condition to the TAM condition.
These and other features and advantages will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative implementations in conjunction with the drawings.